bims-lypmec 2023-08-13 papers

Issue of 2023‒08‒13
five papers selected by
Satoru Kobayashi
New York Institute of Technology

Nat Cell Biol. 2023 Aug 10.

Malonyl-CoA is a conserved endogenous ATP-competitive mTORC1 inhibitor.

Raffaele Nicastro, Laura Brohée, Josephine Alba, Julian Nüchel, Gianluca Figlia, Stefanie Kipschull, Peter Gollwitzer, Jesus Romero-Pozuelo, Stephanie A Fernandes, Andreas Lamprakis, Stefano Vanni, Aurelio A Teleman, Claudio De Virgilio, Constantinos Demetriades.

Cell growth is regulated by the mammalian/mechanistic target of rapamycin complex 1 (mTORC1), which functions both as a nutrient sensor and a master controller of virtually all biosynthetic pathways. This ensures that cells are metabolically active only when conditions are optimal for growth. Notably, although mTORC1 is known to regulate fatty acid biosynthesis, how and whether the cellular lipid biosynthetic capacity signals back to fine-tune mTORC1 activity remains poorly understood. Here we show that mTORC1 senses the capacity of a cell to synthesise fatty acids by detecting the levels of malonyl-CoA, an intermediate of this biosynthetic pathway. We find that, in both yeast and mammalian cells, this regulation is direct, with malonyl-CoA binding to the mTOR catalytic pocket and acting as a specific ATP-competitive inhibitor. When fatty acid synthase (FASN) is downregulated/inhibited, elevated malonyl-CoA levels are channelled to proximal mTOR molecules that form direct protein-protein interactions with acetyl-CoA carboxylase 1 (ACC1) and FASN. Our findings represent a conserved and unique homeostatic mechanism whereby impaired fatty acid biogenesis leads to reduced mTORC1 activity to coordinately link this metabolic pathway to the overall cellular biosynthetic output. Moreover, they reveal the existence of a physiological metabolite that directly inhibits the activity of a signalling kinase in mammalian cells by competing with ATP for binding.

DOI: https://doi.org/10.1038/s41556-023-01198-6

Nat Commun. 2023 08 08. 14(1): 4765

A conserved membrane curvature-generating protein is crucial for autophagosome formation in fission yeast.

Ning Wang, Yoko Shibata, Joao A Paulo, Steven P Gygi, Tom A Rapoport.

Organelles are shaped by curvature-generating proteins, which include the reticulons and REEPs that are involved in forming the endoplasmic reticulum (ER). A conserved REEP subfamily differs from the ER-shaping REEPs in abundance and membrane topology and has unidentified functions. Here, we show that Rop1, the single member of this family in the fission yeast Schizosacharomyces pombe, is crucial for the macroautophagy of organelles and cytosolic proteins. Rop1 is needed for the formation of phagophores, cup-like structures consisting of two closely apposed membrane sheets that encapsulate cargo. It is recruited at early stages to phagophores and is required for their maturation into autophagosomes. Rop1 function relies on its ability to generate high membrane curvature and on its colocalization with the autophagy component Atg2 that is thought to reside at the phagophore rim. We propose that Rop1 facilitates the formation and growth of the double-membrane structure of the autophagosome.

DOI: https://doi.org/10.1038/s41467-023-40530-4

Autophagy. 2023 Aug 06. 1-4

Activated STING1 rides the Rafeesome.

Yaping Han, Jianfei Zheng, Liang Ge.

Over the past decade, accumulated studies have reported the presence of non-canonical macroautophagy/autophagy characterized by the shared usage of the autophagy machinery and distinct components that function in multiple scenarios but do not involve lysosomal degradation. One type of non-canonical autophagy is secretory autophagy, which facilitates the secretion of various cargoes. In a recent work from Gao et al. the ER-membrane protein STING1 has been identified as a novel substrate of secretory autophagy. The secretion of activated STING1 is mediated by its packing into the rafeesome, a newly identified organelle formed upon the fusion of RAB22A-mediated non-canonical autophagosome with an early endosome. Moreover, extracellular vesicles containing activated STING1 induce antitumor immunity in recipient cells, a process potentially promoted by RAB22A.

Keywords: Autophagosome; ERGIC; RAB22; Rafeesome; STING; Unconventional secretion

DOI: https://doi.org/10.1080/15548627.2023.2240154

J Am Chem Soc. 2023 Aug 08.

Harnessing the Lysosomal Sorting Signals of the Cation-Independent Mannose-6-Phosphate Receptor for Targeted Degradation of Membrane Proteins.

Jinfeng Yu, Haonan Li, Tong Fang, Chengyu Yun, Xue Liu, Jingyao Xu, Xianxing Jiang, Xiaoqing Cai.

Membrane proteins are a crucial class of therapeutic targets that remain challenging to modulate using traditional occupancy-driven inhibition strategies or current proteolysis-targeting degradation approaches. Here, we report that the inherent endolysosomal sorting machinery can be harnessed for the targeted degradation of membrane proteins. A new degradation technique, termed signal-mediated lysosome-targeting chimeras (SignalTACs), was developed by genetically fusing the signaling motif from the cation-independent mannose-6-phosphate receptor (CI-M6PR) to a membrane protein binder. Antibody-based SignalTACs were constructed with the CI-M6PR signal peptides fused to the C-terminus of both heavy and light chains of IgG. We demonstrated the scope of this platform technology by degrading five pathogenesis-related membrane proteins, including HER2, EGFR, PD-L1, CD20, and CD71. Furthermore, two simplified constructs of SignalTACs, nanobody-based and peptide-based SignalTACs, were created and shown to promote the lysosomal degradation of target membrane proteins. Compared to the parent antibodies, SignalTACs exhibited significantly higher efficiency in inhibiting tumor cell growth both in vitro and in vivo. This work provides a simple, general, and robust strategy for degrading membrane proteins with molecular precision and may represent a powerful platform with broad research and therapeutic applications.

DOI: https://doi.org/10.1021/jacs.3c07687

JACC Basic Transl Sci. 2023 Jul;8(7): 884-904

Immunometabolism at the Heart of Cardiovascular Disease.

Matthew DeBerge, Rajesh Chaudhary, Samantha Schroth, Edward B Thorp.

Immune cell function among the myocardium, now more than ever, is appreciated to regulate cardiac function and pathophysiology. This is the case for both innate immunity, which includes neutrophils, monocytes, dendritic cells, and macrophages, as well as adaptive immunity, which includes T cells and B cells. This function is fueled by cell-intrinsic shifts in metabolism, such as glycolysis and oxidative phosphorylation, as well as metabolite availability, which originates from the surrounding extracellular milieu and varies during ischemia and metabolic syndrome. Immune cell crosstalk with cardiac parenchymal cells, such as cardiomyocytes and fibroblasts, is also regulated by complex cellular metabolic circuits. Although our understanding of immunometabolism has advanced rapidly over the past decade, in part through valuable insights made in cultured cells, there remains much to learn about contributions of in vivo immunometabolism and directly within the myocardium. Insight into such fundamental cell and molecular mechanisms holds potential to inform interventions that shift the balance of immunometabolism from maladaptive to cardioprotective and potentially even regenerative. Herein, we review our current working understanding of immunometabolism, specifically in the settings of sterile ischemic cardiac injury or cardiometabolic disease, both of which contribute to the onset of heart failure. We also discuss current gaps in knowledge in this context and therapeutic implications.

Keywords: heart failure; immunometabolism; myocardial infarction

DOI: https://doi.org/10.1016/j.jacbts.2022.12.010